H.M.O. requirement, usually

• Patient's share of a bill
• Number on a health-insurance card
• Cost of a visit
• Fee for many a doctor's visit
• Charge for visiting the doctor
• Patient's liability
• One's share of a medical bill, maybe
• Consultation cost, perhaps
• Chip-in at a doc's office

Wiktionary Word definitions in Wiktionary
n. A copayment. vb. To jointly pay with another or others.